EP3718724B1

EP3718724B1 - Method for recycling plastic nylon 6,6 from vacuum bags to obtain filaments for 3d printing processes

Info

Publication number: EP3718724B1
Application number: EP19382254.1A
Authority: EP
Inventors: Enrique Guinaldo Fernandez; Tamara BLANCO VARELA; Guillermo HERNAIZ LOPEZ; José Sanchez Gomez
Original assignee: Airbus Operations SL
Current assignee: Airbus Operations SL
Priority date: 2019-04-05
Filing date: 2019-04-05
Publication date: 2023-05-31
Anticipated expiration: 2039-04-05
Also published as: EP3718724A1; US12594694B2; US20220184857A1; WO2020201609A1; ES2949328T3; CN113692336A

Description

Field of the invention

The invention refers to methods for recycling plastic Nylon 6,6 from vacuum bags to obtain filaments for 3D printing of plastics, for instance by using Fused Filament Fabrication (FFF) printers and/or Selective Laser Sintering (SLS) printers.
3D printed aeronautical flying or non-flying parts can be produced with recycled filaments or powder. As examples of non-flying parts, tools or other manufacturing elements can be included.

Background of the invention

Nowadays raw plastics which are base of the Fused Filament Fabrication (FFF) filaments or the powder for Selective Laser Sintering (SLS) processes are obtained from virgin materials. The same situation is observed for the fibre reinforcements: they are obtained from the classical manufacturing methods known for the raw fibres.
Currently, there is not any process or procedure for the recycling of vacuum bags which are extensively used for curing processes of prepreg materials and/or vacuum based infusion processes such as LRI, VARTM, RFI, etc.
Nevertheless, there are some methods and processes for the recycling of polyamides. As Nylon 6,6, the material that vacuum bags are made of, is part of the polyamides family, this opens the possibility of finding a second life for this material that is extensively used in the composites industry and can be re-used in other applications.
So far, current methods for recycling polyamides carry out processes of depolymerisation and repolymerisation, as disclosed in the following patent documents:

US 8366977 B2 : Process of making recycled polyamide yarn.
US 2004/0249001 A1 : Process for the solution recovery of nylon with high reactivity and articles made therefrom.
US 6187917 B1 : Process for the purification of caprolactam obtained from the depolymerasation of polyamide-containing carpet.
US 2004/0186190 A1 : Solvent-based recovery and recycle polyamide material.

EP 3012078 A1 discloses a process that uses a starting material formed by recycled post-consumer and industrial "scrap" thermoplastics based on polyester and polyamide, and obtains a supply suitable for 3D printing/additive manufacturing/rapid prototyping with "Fused Deposition Model" (FDM), "Fused Filament Fabrication" (FFF) from these recycled thermoplastics. Said supply can have the form of a solid filament suitable to be used by said "3D" printers, or it can form a pulverulent material to be used in printers such as those with SLS technology. The method includes a series of first stages that consist of: a) Selecting the starting material, which was originally produced by one of the processes of transformation; b) said starting material is duly cleaned; c) once it is cleaned, the material is dried at temperatures greater than 100 ºC but less than 240 ºC; d) the material obtained thereof is driven into an extruder machine where it is subject to temperatures that will vary between 200 °C and 350 °C from the head to the dosing zone to be pelletized; e) the addition of additives to the material may occur in the feed zone in order to grant distinctive physicochemical properties to the end product, such as colour, hardness, erosion, strength f) from the material resulting from the previous stage either a plastic filament is created and is placed in a spool, or a pulverulent material is created. The supply obtained from the previous stages is subject to an additional heat treatment by varying the process temperature between 100 ºC and 240°C, during a processing time varying between 1 minute and 24 hours.
Regarding recycled reinforcement fibres, currently there are developed processes for obtaining fibres from carbon fibre reinforced processes like the pyrolysis or the solvolysis. These activities are acquiring more importance due to the interest of several industries, like the automotive one.
However, so far these reinforcements are not used to reinforce Additive Manufacturing filaments, they are mostly used for non-highly loaded components manufactured by short fibre reinforcement moulding.
Currently, Nylon 6,6 is used without being combined and with short-fibre reinforcement for parts with no structural requirements in aircraft manufactured by classical methods, for example machining a round bar. In addition, it is used in the aeronautics industry for the design of prototypes and models as well as for the fabrication of drill templates.
Nowadays, one of the main issues associated to the increase of composite parts in aircrafts is the amount of material scrap / waste obtained in production plants, which highly affects part life cycle:

Auxiliary materials / vacuum bags: during part curing processes (Autoclave or OoA), a large amount of vacuum bags are needed, which are thrown away once curing processes are performed.
Composite / fibre reinforced plastics (FRP) scrap: in addition, tons of CFRP scrap are obtained during part production, which are nowadays mostly buried.

In fact, this problem could be greater in the future with the expected environmental regulation changes, which may limit material waste. Therefore solutions are needed as soon as possible to reduce and/or recycle the material waste obtained in composite part production.
On the other hand, 3D printing (also known as Additive Manufacturing) is a technology with high advantages for application in aeronautical or other fields, which is now being widely developed and explored to get the full potential of it. Particularly, plastics and reinforced plastics 3D printing are making their way in the market and showing also high potential for different applications (e.g. low loaded parts).

Summary of the invention

The invention relates to a method in accordance with claim 1.
Dependent claims refer to preferred embodiments of the invention.
In particular, the object of the invention is to provide methods for recycling plastic Nylon 6,6 from vacuum bags (for example, those used in aircraft part production) to obtain filaments for 3D printing processes, such that the scrap materials obtained in the production of composite parts can be reduced.
The invention provides a method for recycling plastic Nylon 6,6 from vacuum bags to obtain filaments for 3D printing processes, that comprises the following steps:

providing used Nylon 6,6 vacuum bags,
quality control step to check the status of the used vacuum bags,
step to form smaller parts from the used vacuum bags:
- the vacuum bags are cut into films, the films are rolled up and then are introduced into a set of extruder and cutter to obtain pellets,
quality control step to check the status of the pellets,
extrusion step: the pellets are introduced into an extruder, where they are melted, and the molten mixture is cooled and expelled through the die of the extruder to produce the recycled filaments, and
winding step: the recycled filaments that go out of the extruder are rolled up in coils.

The invention presents several advantages, related to the recycling of a material, which is supposed to be used just once, for an innovative application / use (3D printing):

Positive environmental impact / life Cycle assessment:
- ∘ Recycling Nylon 6,6 of the vacuum bag allows the bag to be reused for a completely different and innovative target from the previous one.
- ∘ Reinforcements from fibre reinforced plastics can be reused by introducing them in the product life cycle again instead of burying them.
- ∘ Make 3D printing processes more attractive from environmental point / life cycle assessment of view.
Positive economic / cost impact:
- ∘ Mitigate the costs of new plastics and reinforcements purchase, raw materials for the 3D printing processes / parts.
- ∘ Mitigate the costs both economical and of brand image of waste production and treatment.
- ∘ Potential sales of a recycled product to other industries (outside aerospace field).

Other characteristics and advantages of the present invention will be clear from the following detailed description of several embodiments illustrative of its object in relation to the attached figures.

Brief description of drawings

Figure 1A shows a schematic diagram of the method for recycling plastic Nylon 6,6 from vacuum bags to obtain unreinforced filaments for 3D printing processes, in a first alternative, which does not fall within the scope of the claims.
Figure 1B shows a schematic diagram of the method for recycling plastic Nylon 6,6 from vacuum bags to obtain unreinforced filaments for 3D printing processes of the invention, in a second alternative.
Figure 2 shows a schematic representation of a grinder machine of figure 1A.
Figure 3 shows a schematic representation of an extruder of figure 1A.
Figure 4 shows a schematic representation of a winder of figure 1A or 1B and the winding process.
Figure 5A shows a schematic diagram of the method for recycling plastic Nylon 6,6 from vacuum bags to obtain reinforced filaments for 3D printing processes, in a first alternative, which does not fall within the scope of the claims.
Figure 5B shows a schematic diagram of the method for recycling plastic Nylon 6,6 from vacuum bags to obtain reinforced filaments for 3D printing processes of the invention, in a second alternative.
Figure 6 shows a schematic diagram of the method for recycling plastic Nylon 6,6 from vacuum bags to obtain powder for 3D printing processes, which does not fall within the scope of the claims.

Detailed description of the invention

The invention refers to methods for recycling plastic Nylon 6,6 from vacuum bags 2 (for example, those used in aircraft part production) to obtain filaments 9 or powder for 3D printing processes, particularly for the production of aircraft parts.
The filaments 9 are used for Fused Filament Fabrication (FFF) and the powder for Selective Laser Sintering (SLS).

A) Filament Manufacturing.

Recycled filaments 9 may be obtained with or without reinforcement from production vacuum bags 2 and CFRP scraps.
The process / steps to be followed to recycle vacuum bag 2 (Nylon 6,6), including the 3D printing filament production, are described hereafter:

Providing used

Nylon

6,6 vacuum bags 2.

Quality Control Step:

In order to control if vacuum bags 2 have suffered any kind of problem, a quality control step is needed. This control should be performed periodically, including visual inspection to detect any change of colour, appearance, rigidity or flexibility that involves crystallinity degree modification, and/or concentration of resin residues, and thermal analysis, such as Thermogravimetry (TMA), to detect potential effect in different parameters, such as weight loss percentage.
Moreover, a quality control may be performed periodically at the end of the recycling process to check out if the final product (filament) has the specified / needed properties for the application.

Step to form smaller parts from the used vacuum bags:

Once vacuum bags 2 have been used for curing processes (Autoclave or OoA: Out-of-Autoclave), and after being analysed (if needed), they are picked up and they can:

a) (which does not fall under the scope of the present invention) Be brought into a grinder 1 where they are cut up in smaller minute pieces 3 (for instance, 0,5x0,5cm) that lead to a quicker melting due to their larger superficial area. Different piece sizes can be considered depending on the overall areal weight of the vacuum bag 2 material.
This process is almost immediate, thus, as the vacuum bags 2 go into the grinder 1, the small cut pieces 3 leave the grinder 1 in a non-stop process. Hence, the length of this step depends on the number of used vacuum bags 2 and in case of mixing, on the quantity of virgin Nylon 6,6 which follows the same procedure, or:
b) Be cut into films, then the films are rolled up and then are introduced into a set of extruder and cutter to obtain pellets.

As indicated, the process of adding virgin material is not mandatory, but helps to improve the quality of the re-used material.

Quality Control Step

A quality control of the smaller pieces 3 or the pellets is performed after the previous step. This quality control step comprises one or more of the following controls:

thermal analysis, such as Differential Scanning Calorimetry (DSC), to detect changes in Glass Transition Temperature (Tg), melting temperature (Tm) or extent of crystallinity, and
molecular weight analysis, such as Gel Permeation Chromatography (GPC).

Extrusion Step:

The smaller pieces 3 or the pellets are introduced in an extruder 15 with a motor 8 for the purpose of producing the filaments 9. To do so, the smaller pieces 3 or the pellets go through a hopper 4 and they are melted in the central part of the extruder 15 (Barrel 5 and Screw 6) at a temperature above the melting temperature of Nylon 6,6 (≈273 ºC). As indicated, cut virgin Nylon 6,6 can also be added (for example, in a 50:50 proportion, or in any other proportion) and melted together. Finally, the melt/molten mixture is expelled from the extruder 15 by the die 7, which shapes the melt/molten mixture in the planned filaments 9 (1.75-3 mm diameter) due to the drop of temperature. As for the first step, the length of this step depends on the number of used vacuum bags 2 that provide the small cut pieces 3 or the pellets and on the quantity of needed virgin Nylon 6,6 in case of mixing.
The outdoor temperature or a cooler facilitates the cooling and the solidification right after the die 7. Furthermore, the filaments 9 can also be dyed later.
In the first step, virgin Nylon 6,6 could also be added together with the vacuum bags 2 (for example, in a 50:50 proportion, or in any other proportion) to the same grinder 1 and then melted together.
As mentioned, filaments 9 can be reinforced adding different fibres such us carbon, glass or aramid fibres or other reinforcements such as CNTs, Graphene, carbon black, nanoparticles, etc. Relevant for this proposal is the introduction of recycled fibres (for example, Recycled Short Fibre: Recycled SF in figures 5A and 5B) coming from fibre reinforced plastics scrap obtained during aeronautical part production, through standard process of pyrolysis or solvolysis and applying also a grinding/cutting process to obtain cut fibre, that needs to be fed also to the extrusion process in combination with the plastic, Nylon 6,6, smaller pieces 3 or the pellets.
The reinforcement can be obtained in a compounding step before the extrusion step, in which the smaller pieces 3 or the pellets and fibre reinforcements are introduced in a set of extruder and cutter for the compounding step to obtain reinforced smaller pieces or reinforced pellets to be used in the extrusion step.
Tests conducted adding different fibre percentages in weight were carried out satisfactory, 30% and 40% trials are prepared.

Winding Step:

As the recycled Nylon 6,6 filaments 9 go out of the extruder 15 reinforced or unreinforced, they are rolled up in coils 10 by using a winding process. In order to be placed in the 3D printing device, each coil 10 has to have around 270 meters of filament 9 rolled up on itself.
Figure 4 shows a schematic representation of a winder 16 with an intermediate pulley 11, a pulley 12, a motor 13 and a tension bearing 14, and the winding process.

B) Powder manufacturing (figure 6):

The following steps describe the process used to recycle the vacuum bag 2 material (Nylon 6,6) as 3D printing powder material:

Providing used

Nylon

6,6 vacuum bags 2.

Quality Control Step:

In order to control if vacuum bags 2 have suffered any kind of problem, a quality control step is needed. This control should be performed periodically, including: visual inspection to detect any change of colour, appearance, rigidity or flexibility that involves crystallinity degree modification, and/or concentration of resin residues, and thermal analysis, such as Thermogravimetry (TMA), to detect potential effect in different parameters, such as weight loss percentage.
Moreover, a quality control may be performed periodically at the end of the recycling process to check out if the final product (powder) has the specified properties.

Grinding Step:

After curing processes and being analysed (if needed), vacuum bags 2 are brought into a grinder 1 that produces very little pieces (powder with particles of 0.1 mm diameter) by cutting them up.
Used vacuum bags 2 could also be mixed (in a 50:50 proportion, or in any other proportion) with virgin Nylon 6,6 to improve the quality of the used material, providing as well powder particles with 0,1 mm diameter.
Additionally, during this step recycled Nylon/ virgin Nylon 6,6 can also be mixed in the desired proportion with small pieces of Carbon or Glass Fibres as well as any other reinforcements, recycled (obtained from CFRP scrap through pyrolysis or solvolysis and cutting/grinding process to obtain powder) or not-recycled.

Quality Control Step

A quality control of the powder is performed after the grinding step. This quality control step comprises one or more of the following controls:

The resulting powder is ready to be used in 3D SLS printers.
The mixing could be performed at the same time inside the same grinder 1 or each material could be cut up in a different grinder and then the provided powders would be mixed (50:50).
Additive manufacturing by means of FFF technology with recycled filaments 9 seems to be a good option for non-loaded applications with low rate production or where high NRC investments are required. Additive manufacturing technology appears as a better option versus other technologies (injection moulding...) for these applications.

Claims

Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, that comprises the following steps:
- providing used Nylon 6,6 vacuum bags (2),

- quality control step to check the status of the used vacuum bags (2),

- step to form smaller parts from the used vacuum bags:
- the vacuum bags (2) are cut into films, the films are rolled up and then are introduced into a set of extruder and cutter to obtain pellets,

- quality control step to check the status of the pellets,

- extrusion step: the pellets are introduced into an extruder (15), where they are melted, and the molten material is cooled and expelled through the die (7) of the extruder (15) to produce the recycled filaments (9), and

- winding step: the recycled filaments (9) that go out of the extruder (15) are rolled up in coils (10).
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to claim 1, that additionally comprises a compounding step before the extrusion step, in which the pellets and fibre reinforcements are introduced in a set of extruder and cutter for the compounding step to obtain reinforced pellets to be used in the extrusion step.
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to claim 1, that additionally comprises the addition of fibre reinforcements in the extruder (15) to obtain reinforced filaments (9).
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to any of the previous claims, that additionally comprises the addition of an anti-hydrolysis additive into the set of extruder and cutter to avoid humidity absorption in the step to form smaller parts to obtain pellets.
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to claims 2 or 3, wherein the fibre reinforcements are virgin fibres.
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to claim 2, wherein the fibre reinforcements are recycled fibres obtained from fibre reinforced plastics scraps obtained during aircraft part production.
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to claim 6, wherein the recycled fibres are obtained through a process of pyrolysis or solvolysis followed by a grinding or cutting process to obtain cut fibre.
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to any of the previous claims, that additionally comprises the addition of virgin Nylon 6,6 in the step to form smaller parts from the used vacuum bags and/or in the extruder (15).
Method for recycling plastic Nylon 6,6 from vacuum bags (2) to obtain filaments (9) for 3D printing processes, according to any of the previous claims, in which the quality control step to check the status of the used vacuum bags (2) comprises one or more of the following controls:
- visual inspection to detect any change of colour, appearance, rigidity or flexibility that involves crystallinity degree modification and/or concentration of resin residues, and

- thermal analysis, such as Thermogravimetry, to detect weight loss percentage,
and the quality control step to check the status of the cut pieces (3) before the extrusion step comprises one or more of the following controls:
- thermal analysis, such as Differential Scanning Calorimetry, to detect changes in Glass Transition Temperature, melting temperature or extent of crystallinity, and

- molecular weight analysis, such as Gel Permeation Chromatography.